“Normal” Disabilities

The brain shapes our inner reality, and in my previous post I discussed the way neurological damage can distort our reality-sense. I offer other examples in Your Living Mind. But those of us who are “normal” also experience the world in ways that are irrational. Scientists are discovering more and more ways in which normal humans suffer from perceptual disabilities. Perception does not just duplicate the outside world, as if we were photocopy machines.

One example of a normal disability is inattentional blindness. It may seem as if we would surely be aware of anything we’re looking at directly. But if people are paying attention to one thing they may not see something else, even if they are gazing straight at it. In one study subjects were asked to stare at a fixed point, but they had to report whenever an X appeared a few inches away from the point they were gazing at. So they were looking at one point but staying alert for randomly appearing Xs nearby. Partway through this task, without warning, some letter or shape would appear at the fixation point, right where they were looking. Many did not see what unexpectedly appeared, even though they were looking right at it!

Interestingly, some kinds of items were usually noticed. “The two most reliable of this small group of attention-capturing stimuli are one’s own name and the iconic representation of a happy face” (Arien Mack, “Is the Visual World a Grand Illusion? A Response,” Journal of Consciousness Studies, May/June, 2002, p. 108). But if even one vowel in the name is incorrect, we are unlikely to detect it, “suggesting that it is the meaning of the stimulus that captures attention and not some lower-level stimulus attribute” (p. 109). After information about what we are staring at travels up the optic nerve into our brains, cerebral sentries note the significance of this perceptual data, and decide whether to let it become conscious.

Here’s a frightening example of inattentional blindness. Pilots in training use a simulator to practice flying while they’re safely on the ground, watching a screen that duplicates what they would see out the windshield of an aircraft. At one point NASA was testing a display that projects navigational information onto the windshield, as if the information were floating out in front of the airplane. Sometimes pilots were “using a display, commenting on how nice it was, while landing their aircraft right on top of another aircraft taxiing onto their runway in plain view” (Daniel Levin, “Change Blindness Blindness As Visual Metacognition,” Journal of Consciousness Studies, May/June, 2002, p. 127). Their attention was on the new display, so they overlooked a huge moving obstacle right in front of them!

Roger Christan Schriner


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